1. Field of the Invention
The present invention relates to a process of producing a vinyl chloride polymer, in particular to a process of producing a vinyl chloride polymer having a high bulk density and a high porosity and therefore capable of producing an extruded product of high quality with an extremely small number of fish eyes, at high efficiency and high productivity.
2. Description of the Prior Art
Heretofore, in extruding a vinyl chloride polymer to form a rigid extrudate, a polymer with a high bulk density is required to enhance productivity, i.e., extrusion rate. On the other hand, high porosity is required for polymers so that the polymer may have good gelling properties and good plasticizer take up. Hence, various attempts have been so far made to produce a vinyl chloride polymer having a high bulk density as well as a high porosity. However, increase in bulk density and increase in porosity of a vinyl chloride polymer are in conflict with each other; therefore it has been extremely difficult to satisfy both requirements simultaneously.
Recently, to solve this problem, methods have been proposed in which a water-insoluble crosslinked polymer containing a carboxyl group and a nonionic surfactant are used as dispersants in polymerization of monomers such as vinyl chloride (Japanese Pre-examination Patent Publication (KOHYO) Nos. 500614/1982 and 500650/1982 and Japanese Pre-examination Patent Publication (KOKAI) Nos. 91205/1986 and 14204/1986).
However, the methods described in the Japanese Pre-examination Patent Publication (KOHYO) Nos. 500614/1982 and 500650/1982 can produce a polymer with a high bulk density to a certain extent, but can achieve a high porosity which is necessary to produce extrudates with no fish eyes, with difficulty. On the other hand, the methods described in the Japanese Pre-examination Patent Publication (KOKAI) Nos. 91205/1986 and 14204/1986 can produce polymers with a high bulk density and an increased porosity. However, in the case where the amount of monomers charged is increased or the polymerization time is shortened, the polymerization reaction becomes unstable, resulting in an agglomerated polymer; thus the methods have the problem that it is impossible to produce a vinyl chloride polymer of high quality in regard to bulk density, particle size distribution and the number of fish eyes in extruded products, at high efficiency and high productivity.